from May 2012 ( From my research the marginal cost of production have increased since that report)
HIGHLIGHTS: Our analysis of the 50 largest publically traded oil and gas companies (ex-FSU) shows that cost inflation continues to increase sharply within the global upstream oil and gas industry. In 2011, production costs increased by 26% while the unit cost of production increased by 21%, which was higher than longer term trends. In 2011, the marginal cost of production the same companies increased 10.8% to US$92.26/bbl............for more read the complete pdf