HOUSTON — Guyana, the tiny English-speaking South American country, is poised to become the next big oil producer in the Western Hemisphere, attracting the attention and investment dollars of some of the biggest oil companies in the world.

This week, Exxon Mobil and Hess announced the successful drilling of a deepwater exploration well that may soon confirm that the seafloor beneath Guyana’s coastal waters contains one of the richest oil and natural gas discoveries in decades. Experts now estimate that one of its offshore fields alone, known as Liza, could contain 1.4 billion barrels of oil mixed with natural gas, comparable to some of the larger fields drilled in South America.

With a population of fewer than one million people, Guyana — Venezuela’s eastern neighbor on the continent’s north coast — would be able to export nearly all of the oil that it will begin producing, probably starting around 2020.

The company announcements came only days after the Guyanese government announced its intention to build a $500 million petroleum processing and service center on Crab Island, an enormous investment for one of the poorest countries in the region.