Contact the Okla. Corporation Commission and ask them for info regarding how to deal with an old oil spill. See links below. But understand they may try to take control of the problem and fix it their way. You can not just move oil contaminated dirt to some other place . It has to go to an approved haz. materials/oil field disposal site ($$$).

http://www.occ.state.ok.us/Divisions/OG/ogpa.htm

http://www.occ.state.ok.us/Divisions/OG/Ogold.htm