Abstract Mass grading of a hillside residential project within the Brea-Olinda oil field in southern California provided an opportunity to mitigate the naturally occurring oil and gas seeps at the site during the grading process. Multiple strategies, such as subsurface collection and venting systems, were used to reduce the potential for oil seeps to form in graded lots, and to prevent hazardous accumulations of methane gas in homes. Monitoring of the systems will be conducted by an environmental consultant in accordance with maintenance manuals prepared for the project.