NEW YORK/MEXICO CITY, Dec 11 (Reuters) - Mexico is wrapping up purchases for the 2021 edition of an oil hedging program that insures its revenues from oil sales, sources familiar with the legendarily opaque trade said, following a particularly challenging year. Negotiations to purchase the bulk of the financial contracts that protect Mexico against oil price crashes have now been concluded or are nearing conclusion, two sources with direct knowledge of the matter and three market sources who follow volumes and flows of such contracts closely said. The Mexican finance ministry declined to comment. (Reporting by Devika Krishna Kumar in New York and Stefanie Eschenbacher in Mexico City Editing by Frank Jack Daniel and Marguerita Choy)