Chevron is buying Anadarko Petroleum for $33 billion, energizing its oil and gas drilling capabilities in Texas and the Gulf of Mexico while vaulting itself into a new league.

The combined company will remain far behind Exxon Mobil Corp. and Royal Dutch Shell Plc. in market capitalization, but Chevron will jump from being the world's fourth biggest energy producer, to second, according to Wood Mackenzie.

"Chevron now joins the ranks of the UltraMajors - and the big three becomes the big four," wrote Roy Martin, senior analyst at Wood Mackenzie, referring to Exxon, Shell and BP.

The cash-and-st...