By Anna Driver HOUSTON, July 2 (Reuters) - Exxon Mobil Corp is contemplating participation in an oil and gas tender of six blocks in northern Afghanistan, a company spokesman said on Monday. Access to the world's oil reserves for companies like Exxon has gotten tougher in recent years as governments assert tighter control of their resources. Opportunity exists, however, in countries like Afghanistan or Iraq where foreign oil companies' budgets and expertise are needed. "Esso Exploration International Ltd's expression of interest in the Afghan-Tajik Basin tender is part of our ongoing evaluation of oil and gas resources around the world," Alan Jeffers, a spokesman for Exxon, said. Afghanistan is seeking bidders for the exploration, development and production of oil and gas in six blocks in the western portion of the Afghan-Tajik Basin of northern Afghanistan, according to its Web site. Bids are due in late October and winning bidders will be announced in late 2012, the government said. Afghanistan signed a deal late last year with China National Petroleum Corp (CNPC) for the development of oil blocks in the Amu Darya basin in the north, a project expected to earn billions of dollars over two decades for the wartorn state. That agreement was the first international oil production agreement reached by the Afghan government for several decades. Shares of Exxon fell 68 cents to $84.88 in midday New York Stock Exchange trading. The energy sector was broadly lower on a $2 per barrel decline in crude oil prices.