PITTSBURGH — Shell Oil has chosen a site in Beaver County for a major, multi-billion-dollar petrochemical refinery that could provide a huge economic boost to the region.

Dan Carlson, Shell's general manager of new business development, said today that the company signed a land option agreement with Horsehead Corp. to evaluate a site near Monaca, about 35 miles northwest of Pittsburgh.

Ohio, West Virginia and Pennsylvania had all sought the plant and offered Shell major tax incentives. Monaca is just 20 miles from both the Ohio and West Virginia borders, so workers in all three states are likely to benefit.

Shell has said that it could spend several billion dollars to build the plant, and that the complex would attract a wide range of industry and suppliers to nearby locations. But actual construction is still years away. The company said the next steps are environmental and design studies and further economic analysis, then permits.