NEW YORK – Exxon said Thursday that it will spend about $150 billion over the next five years to find more oil and natural gas to satisfy the world’s growing energy appetite.

Exxon Mobil Corp., the world’s largest publicly traded energy company, expects global energy demand to increase 30 percent by 2040, compared with 2010 levels. As demand grows, CEO Rex Tillerson said Exxon will plow more money into a global search for new resources. Including investments in its refining and chemicals business, Exxon’s capital budget for 2012 through 2016 will total $185 billion, up 29 percent from the prior five-year period.

While pledging to boost spending, Exxon at the same time cut its long-term expectation for average annual production growth to 2-3 percent, from a previous forecast of 4-5 percent, Tillerson told analysts at the New York Stock Exchange. Exxon’s production could fall by 3 percent this year, after rising just 1 percent in 2011.

This highlights a key challenge for the oil and gas industry: It’s spending increasing amounts of money to achieve marginally higher, if not lower, rates of production.

Major oil companies are struggling to tap new sources of oil fast enough in an environment where big finds are rarer and costlier to exploit. Potential fields lie deep under the seabed, or in shale rock formations that require expensive technology to crack open.

The cost to produce a barrel “clearly is going up,” Tillerson said, with “the size, the magnitude and the conditions with which we’re making some of these investments.”

When companies can’t find oil fast enough, they’re stuck with aging fields where output is declining. International production agreements also limit the amount of oil they can sell as prices rise.

Chevron Corp., BP and Royal Dutch Shell all produced less oil last year than in the prior year. Exxon and the others have in the past few years increasingly focused on developing natural gas.