diff --git a/README.md b/README.md
index a85fbd01d..5a4080915 100644
--- a/README.md
+++ b/README.md
@@ -170,6 +170,7 @@ You can customize the processing with additional optional arguments:
 
 ```
 --model                 LLM model to use (default: gpt-4o-2024-11-20)
+--base-url              Base URL for OpenAI-compatible API providers
 --toc-check-pages       Pages to check for table of contents (default: 20)
 --max-pages-per-node    Max pages per node (default: 10)
 --max-tokens-per-node   Max tokens per node (default: 20000)
@@ -179,6 +180,36 @@ You can customize the processing with additional optional arguments:
 ```
 </details>
 
+<details>
+<summary>OpenAI-compatible API base URL</summary>
+<br>
+PageIndex uses LiteLLM for local LLM calls. To point requests at an OpenAI-compatible endpoint, set `OPENAI_BASE_URL` or pass `--base-url`:
+
+```bash
+OPENAI_BASE_URL=http://localhost:11434/v1
+python3 run_pageindex.py --pdf_path /path/to/your/document.pdf --model openai/llama3.1
+```
+
+You can also pass the endpoint directly:
+
+```bash
+python3 run_pageindex.py --pdf_path /path/to/your/document.pdf \
+  --model openai/llama3.1 \
+  --base-url http://localhost:11434/v1
+```
+
+The same setting is available from the Python SDK in local mode:
+
+```python
+from pageindex import PageIndexClient
+
+client = PageIndexClient(
+    model="ollama/llama3.1",
+    base_url="http://localhost:11434/v1",
+)
+```
+</details>
+
 <details>
 <summary>Markdown support</summary>
 <br>
diff --git a/pageindex/client.py b/pageindex/client.py
index 806ebb638..67c6b687e 100644
--- a/pageindex/client.py
+++ b/pageindex/client.py
@@ -1,5 +1,7 @@
 # pageindex/client.py
 from __future__ import annotations
+
+import os
 from pathlib import Path
 from .collection import Collection
 from .config import IndexConfig
@@ -16,6 +18,14 @@ def _normalize_retrieve_model(model: str) -> str:
     return f"litellm/{model}"
 
 
+def _configured_openai_base_url() -> str | None:
+    return (
+        os.getenv("OPENAI_BASE_URL")
+        or os.getenv("OPENAI_API_BASE")
+        or os.getenv("CHATGPT_API_BASE")
+    )
+
+
 class PageIndexClient:
     """PageIndex client — supports both local and cloud modes.
 
@@ -24,6 +34,7 @@ class PageIndexClient:
             and local-only params (model, storage_path, index_config, …) are ignored.
         model: LLM model for indexing (local mode only, default: gpt-4o-2024-11-20).
         retrieve_model: LLM model for agent QA (local mode only, default: same as model).
+        base_url: Base URL for OpenAI-compatible LLM endpoints (local mode only).
         storage_path: Directory for SQLite DB and files (local mode only, default: ./.pageindex).
         storage: Custom StorageEngine instance (local mode only).
         index_config: Advanced indexing parameters (local mode only, optional).
@@ -41,11 +52,12 @@ class PageIndexClient:
 
     def __init__(self, api_key: str = None, model: str = None,
                  retrieve_model: str = None, storage_path: str = None,
-                 storage=None, index_config: IndexConfig | dict = None):
+                 storage=None, index_config: IndexConfig | dict = None,
+                 base_url: str = None):
         if api_key:
             self._init_cloud(api_key)
         else:
-            self._init_local(model, retrieve_model, storage_path, storage, index_config)
+            self._init_local(model, retrieve_model, storage_path, storage, index_config, base_url)
 
     def _init_cloud(self, api_key: str):
         from .backend.cloud import CloudBackend
@@ -53,7 +65,11 @@ def _init_cloud(self, api_key: str):
 
     def _init_local(self, model: str = None, retrieve_model: str = None,
                     storage_path: str = None, storage=None,
-                    index_config: IndexConfig | dict = None):
+                    index_config: IndexConfig | dict = None,
+                    base_url: str = None):
+        if base_url:
+            os.environ["OPENAI_BASE_URL"] = base_url
+
         # Build IndexConfig: merge model/retrieve_model with index_config
         overrides = {}
         if model:
@@ -89,14 +105,17 @@ def _validate_llm_provider(model: str) -> None:
         """Validate model and check API key via litellm. Warns if key seems missing."""
         try:
             import litellm
+            from .index.utils import _model_uses_openai_base_url
             litellm.model_cost_map_url = ""
             _, provider, _, _ = litellm.get_llm_provider(model=model)
         except Exception:
             return
 
+        if _configured_openai_base_url() and _model_uses_openai_base_url(model):
+            return
+
         key = litellm.get_api_key(llm_provider=provider, dynamic_api_key=None)
         if not key:
-            import os
             common_var = f"{provider.upper()}_API_KEY"
             if not os.getenv(common_var):
                 from .errors import PageIndexError
@@ -130,6 +149,7 @@ class LocalClient(PageIndexClient):
     Args:
         model: LLM model for indexing (default: gpt-4o-2024-11-20)
         retrieve_model: LLM model for agent QA (default: same as model)
+        base_url: Base URL for OpenAI-compatible LLM endpoints.
         storage_path: Directory for SQLite DB and files (default: ./.pageindex)
         storage: Custom StorageEngine instance (default: SQLiteStorage)
         index_config: Advanced indexing parameters. Pass an IndexConfig instance
@@ -150,8 +170,9 @@ class LocalClient(PageIndexClient):
 
     def __init__(self, model: str = None, retrieve_model: str = None,
                  storage_path: str = None, storage=None,
-                 index_config: IndexConfig | dict = None):
-        self._init_local(model, retrieve_model, storage_path, storage, index_config)
+                 index_config: IndexConfig | dict = None,
+                 base_url: str = None):
+        self._init_local(model, retrieve_model, storage_path, storage, index_config, base_url)
 
 
 class CloudClient(PageIndexClient):
diff --git a/pageindex/index/utils.py b/pageindex/index/utils.py
index f416d6d3d..5b86e97c9 100644
--- a/pageindex/index/utils.py
+++ b/pageindex/index/utils.py
@@ -1,5 +1,6 @@
 import litellm
 import logging
+import os
 import time
 import json
 import copy
@@ -10,6 +11,50 @@
 logger = logging.getLogger(__name__)
 
 
+_OPENAI_BASE_URL_PROVIDERS = {
+    "openai",
+    "openai_like",
+    "custom_openai",
+    "text-completion-openai",
+    "aiohttp_openai",
+    "ollama",
+    "ollama_chat",
+    "lm_studio",
+    "hosted_vllm",
+    "vllm",
+    "llamafile",
+    "xinference",
+    "oobabooga",
+}
+
+
+def _normalize_litellm_model(model):
+    return model.removeprefix("litellm/") if model else model
+
+
+def _model_uses_openai_base_url(model):
+    model = _normalize_litellm_model(model)
+    if not model:
+        return False
+    if "/" in model:
+        provider = model.split("/", 1)[0]
+        return provider in _OPENAI_BASE_URL_PROVIDERS
+    try:
+        _, provider, _, _ = litellm.get_llm_provider(model=model)
+        return provider in _OPENAI_BASE_URL_PROVIDERS
+    except Exception:
+        return True
+
+
+def _litellm_api_base_kwargs(model):
+    api_base = (
+        os.getenv("OPENAI_BASE_URL")
+        or os.getenv("OPENAI_API_BASE")
+        or os.getenv("CHATGPT_API_BASE")
+    )
+    return {"api_base": api_base} if api_base and _model_uses_openai_base_url(model) else {}
+
+
 def count_tokens(text, model=None):
     if not text:
         return 0
@@ -28,6 +73,7 @@ def llm_completion(model, prompt, chat_history=None, return_finish_reason=False)
                 model=model,
                 messages=messages,
                 temperature=0,
+                **_litellm_api_base_kwargs(model),
             )
             content = response.choices[0].message.content
             if return_finish_reason:
@@ -57,6 +103,7 @@ async def llm_acompletion(model, prompt):
                 model=model,
                 messages=messages,
                 temperature=0,
+                **_litellm_api_base_kwargs(model),
             )
             return response.choices[0].message.content
         except Exception as e:
diff --git a/pageindex/utils.py b/pageindex/utils.py
index f00ccf3a7..ea0789a11 100644
--- a/pageindex/utils.py
+++ b/pageindex/utils.py
@@ -23,6 +23,50 @@
 
 litellm.drop_params = True
 
+_OPENAI_BASE_URL_PROVIDERS = {
+    "openai",
+    "openai_like",
+    "custom_openai",
+    "text-completion-openai",
+    "aiohttp_openai",
+    "ollama",
+    "ollama_chat",
+    "lm_studio",
+    "hosted_vllm",
+    "vllm",
+    "llamafile",
+    "xinference",
+    "oobabooga",
+}
+
+
+def _normalize_litellm_model(model):
+    return model.removeprefix("litellm/") if model else model
+
+
+def _model_uses_openai_base_url(model):
+    model = _normalize_litellm_model(model)
+    if not model:
+        return False
+    if "/" in model:
+        provider = model.split("/", 1)[0]
+        return provider in _OPENAI_BASE_URL_PROVIDERS
+    try:
+        _, provider, _, _ = litellm.get_llm_provider(model=model)
+        return provider in _OPENAI_BASE_URL_PROVIDERS
+    except Exception:
+        return True
+
+
+def _litellm_api_base_kwargs(model):
+    api_base = (
+        os.getenv("OPENAI_BASE_URL")
+        or os.getenv("OPENAI_API_BASE")
+        or os.getenv("CHATGPT_API_BASE")
+    )
+    return {"api_base": api_base} if api_base and _model_uses_openai_base_url(model) else {}
+
+
 def count_tokens(text, model=None):
     if not text:
         return 0
@@ -40,6 +84,7 @@ def llm_completion(model, prompt, chat_history=None, return_finish_reason=False)
                 model=model,
                 messages=messages,
                 temperature=0,
+                **_litellm_api_base_kwargs(model),
             )
             content = response.choices[0].message.content
             if return_finish_reason:
@@ -70,6 +115,7 @@ async def llm_acompletion(model, prompt):
                 model=model,
                 messages=messages,
                 temperature=0,
+                **_litellm_api_base_kwargs(model),
             )
             return response.choices[0].message.content
         except Exception as e:
@@ -707,4 +753,3 @@ def print_tree(tree, indent=0):
 def print_wrapped(text, width=100):
     for line in text.splitlines():
         print(textwrap.fill(line, width=width))
-
diff --git a/run_pageindex.py b/run_pageindex.py
index a2d4c3185..9ef27880d 100644
--- a/run_pageindex.py
+++ b/run_pageindex.py
@@ -12,6 +12,8 @@
     parser.add_argument('--md_path', type=str, help='Path to the Markdown file')
 
     parser.add_argument('--model', type=str, default=None, help='Model to use')
+    parser.add_argument('--base-url', '--api-base', dest='base_url', type=str, default=None,
+                      help='Base URL for OpenAI-compatible API providers')
 
     parser.add_argument('--toc-check-pages', type=int, default=None,
                       help='Number of pages to check for table of contents (PDF only)')
@@ -44,6 +46,9 @@
     if args.pdf_path and args.md_path:
         raise ValueError("Only one of --pdf_path or --md_path can be specified")
 
+    if args.base_url:
+        os.environ["OPENAI_BASE_URL"] = args.base_url
+
     # Build IndexConfig from CLI args (None values use defaults)
     config_overrides = {
         k: v for k, v in {
diff --git a/tests/test_client.py b/tests/test_client.py
index 2c78c92cc..9b29b59e3 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -1,4 +1,6 @@
 # tests/sdk/test_client.py
+import os
+
 import pytest
 from pageindex.client import PageIndexClient, LocalClient, CloudClient
 
@@ -49,3 +51,49 @@ class FakeParser:
         def supported_extensions(self): return [".txt"]
         def parse(self, file_path, **kwargs): pass
     client.register_parser(FakeParser())
+
+
+def test_pageindex_client_base_url_configures_local_openai_compatible_backend(monkeypatch, tmp_path):
+    monkeypatch.delenv("OPENAI_BASE_URL", raising=False)
+    monkeypatch.delenv("OLLAMA_API_KEY", raising=False)
+
+    client = PageIndexClient(
+        model="ollama/llama3.1",
+        base_url="http://example.test/v1",
+        storage_path=str(tmp_path / "pi"),
+    )
+
+    assert isinstance(client, PageIndexClient)
+    assert client._backend._model == "ollama/llama3.1"
+    assert os.environ["OPENAI_BASE_URL"] == "http://example.test/v1"
+
+
+def test_local_client_accepts_base_url(monkeypatch, tmp_path):
+    monkeypatch.delenv("OPENAI_BASE_URL", raising=False)
+    monkeypatch.delenv("OLLAMA_API_KEY", raising=False)
+
+    client = LocalClient(
+        model="ollama/llama3.1",
+        base_url="http://example.test/v1",
+        storage_path=str(tmp_path / "pi"),
+    )
+
+    assert isinstance(client, PageIndexClient)
+    assert os.environ["OPENAI_BASE_URL"] == "http://example.test/v1"
+
+
+def test_pageindex_client_accepts_openai_api_base_env_for_local_compatible_backend(
+    monkeypatch,
+    tmp_path,
+):
+    monkeypatch.delenv("OPENAI_BASE_URL", raising=False)
+    monkeypatch.delenv("OLLAMA_API_KEY", raising=False)
+    monkeypatch.setenv("OPENAI_API_BASE", "http://api-base.example/v1")
+
+    client = PageIndexClient(
+        model="ollama/llama3.1",
+        storage_path=str(tmp_path / "pi"),
+    )
+
+    assert isinstance(client, PageIndexClient)
+    assert client._backend._model == "ollama/llama3.1"
diff --git a/tests/test_litellm_api_base.py b/tests/test_litellm_api_base.py
new file mode 100644
index 000000000..76501274b
--- /dev/null
+++ b/tests/test_litellm_api_base.py
@@ -0,0 +1,137 @@
+import asyncio
+from types import SimpleNamespace
+from unittest.mock import AsyncMock, patch
+
+import pytest
+
+
+def _make_response(content="ok"):
+    message = SimpleNamespace(content=content)
+    choice = SimpleNamespace(message=message, finish_reason="stop")
+    return SimpleNamespace(choices=[choice])
+
+
+def test_index_utils_completion_passes_openai_base_url(monkeypatch):
+    from pageindex.index import utils
+
+    monkeypatch.setenv("OPENAI_BASE_URL", "http://example.test/v1")
+
+    with patch.object(utils.litellm, "completion", return_value=_make_response()) as mock_completion:
+        assert utils.llm_completion("gpt-4o", "hello") == "ok"
+
+    assert mock_completion.call_args.kwargs["api_base"] == "http://example.test/v1"
+
+
+def test_index_utils_completion_passes_openai_base_url_for_openai_prefix(monkeypatch):
+    from pageindex.index import utils
+
+    monkeypatch.setenv("OPENAI_BASE_URL", "http://example.test/v1")
+
+    with patch.object(utils.litellm, "completion", return_value=_make_response()) as mock_completion:
+        assert utils.llm_completion("openai/gpt-4o", "hello") == "ok"
+
+    assert mock_completion.call_args.kwargs["api_base"] == "http://example.test/v1"
+
+
+@pytest.mark.parametrize("model", [
+    "ollama/llama3.1",
+    "lm_studio/llama3.1",
+    "hosted_vllm/llama3.1",
+    "litellm/ollama/llama3.1",
+])
+def test_index_utils_completion_passes_openai_base_url_for_compatible_provider_prefixes(
+    monkeypatch,
+    model,
+):
+    from pageindex.index import utils
+
+    monkeypatch.setenv("OPENAI_BASE_URL", "http://example.test/v1")
+
+    with patch.object(utils.litellm, "completion", return_value=_make_response()) as mock_completion:
+        assert utils.llm_completion(model, "hello") == "ok"
+
+    assert mock_completion.call_args.kwargs["api_base"] == "http://example.test/v1"
+
+
+def test_index_utils_completion_omits_openai_base_url_for_anthropic(monkeypatch):
+    from pageindex.index import utils
+
+    monkeypatch.setenv("OPENAI_BASE_URL", "http://example.test/v1")
+
+    with patch.object(utils.litellm, "completion", return_value=_make_response()) as mock_completion:
+        assert utils.llm_completion("anthropic/claude-3-5-sonnet-20241022", "hello") == "ok"
+
+    assert "api_base" not in mock_completion.call_args.kwargs
+
+
+def test_index_utils_completion_omits_openai_base_url_for_gemini(monkeypatch):
+    from pageindex.index import utils
+
+    monkeypatch.setenv("OPENAI_BASE_URL", "http://example.test/v1")
+
+    with patch.object(utils.litellm, "completion", return_value=_make_response()) as mock_completion:
+        assert utils.llm_completion("gemini/gemini-1.5-pro", "hello") == "ok"
+
+    assert "api_base" not in mock_completion.call_args.kwargs
+
+
+def test_index_utils_completion_omits_api_base_by_default(monkeypatch):
+    from pageindex.index import utils
+
+    monkeypatch.delenv("OPENAI_BASE_URL", raising=False)
+    monkeypatch.delenv("OPENAI_API_BASE", raising=False)
+    monkeypatch.delenv("CHATGPT_API_BASE", raising=False)
+
+    with patch.object(utils.litellm, "completion", return_value=_make_response()) as mock_completion:
+        assert utils.llm_completion("gpt-4o", "hello") == "ok"
+
+    assert "api_base" not in mock_completion.call_args.kwargs
+
+
+def test_index_utils_acompletion_passes_openai_api_base(monkeypatch):
+    from pageindex.index import utils
+
+    monkeypatch.delenv("OPENAI_BASE_URL", raising=False)
+    monkeypatch.setenv("OPENAI_API_BASE", "http://api-base.example/v1")
+
+    with patch.object(utils.litellm, "acompletion", new_callable=AsyncMock) as mock_acompletion:
+        mock_acompletion.return_value = _make_response("async ok")
+        result = asyncio.run(utils.llm_acompletion("gpt-4o", "hello"))
+
+    assert result == "async ok"
+    assert mock_acompletion.call_args.kwargs["api_base"] == "http://api-base.example/v1"
+
+
+def test_legacy_utils_completion_passes_chatgpt_api_base(monkeypatch):
+    import pageindex.utils as utils
+
+    monkeypatch.delenv("OPENAI_BASE_URL", raising=False)
+    monkeypatch.delenv("OPENAI_API_BASE", raising=False)
+    monkeypatch.setenv("CHATGPT_API_BASE", "http://legacy.example/v1")
+
+    with patch.object(utils.litellm, "completion", return_value=_make_response()) as mock_completion:
+        assert utils.llm_completion("gpt-4o", "hello") == "ok"
+
+    assert mock_completion.call_args.kwargs["api_base"] == "http://legacy.example/v1"
+
+
+def test_legacy_utils_completion_passes_openai_base_url_for_lm_studio(monkeypatch):
+    import pageindex.utils as utils
+
+    monkeypatch.setenv("OPENAI_BASE_URL", "http://example.test/v1")
+
+    with patch.object(utils.litellm, "completion", return_value=_make_response()) as mock_completion:
+        assert utils.llm_completion("lm_studio/llama3.1", "hello") == "ok"
+
+    assert mock_completion.call_args.kwargs["api_base"] == "http://example.test/v1"
+
+
+def test_legacy_utils_completion_omits_openai_base_url_for_anthropic(monkeypatch):
+    import pageindex.utils as utils
+
+    monkeypatch.setenv("OPENAI_BASE_URL", "http://example.test/v1")
+
+    with patch.object(utils.litellm, "completion", return_value=_make_response()) as mock_completion:
+        assert utils.llm_completion("anthropic/claude-3-5-sonnet-20241022", "hello") == "ok"
+
+    assert "api_base" not in mock_completion.call_args.kwargs