Guyana’s offshore discoveries have helped make Upper Cretaceous reservoirs the world’s most commercially successful exploration targets among the reservoir-age groups assessed by Westwood Global Energy Group.
Jamie Collard, Westwood’s Senior Exploration Research Manager, presented the finding during a mid-year global exploration webinar hosted by the American Association of Petroleum Geologists. He reviewed exploration activity and performance during the first half of 2026.
Westwood examined high-impact wells drilled during the past five years and compared their performance by reservoir age. The company defines a high-impact well as one targeting more than 100 million barrels of oil equivalent in recoverable resources or testing a frontier play.
“What really stands out is the highest commercial success rate has been in the Upper Cretaceous,” Collard said.
Guyana’s prolific offshore discoveries contributed to the performance of that geological interval. ExxonMobil and its Stabroek Block partners have discovered “more than 13 billion barrels of oil equivalent since 2015”, mainly in Upper Cretaceous reservoirs, Westwood said. Exxon puts Guyana’s resource count at 11 billion barrels.
“And there is an impact of Guyana on this,” Collard said. “But actually, if you remove Guyana, it only falls by a couple of percentage points, and it remains the highest commercial success rate.”
He said discoveries in Namibia, Côte d’Ivoire, Angola, onshore Türkiye, and onshore Mexico also supported the Upper Cretaceous result.
Guyana-Suriname Upper Cretaceous play delivered the goods in 2021
The findings show that the interval’s exploration success is not limited to the Guyana-Suriname Basin. However, Guyana remains one of the most significant contributors to global Upper Cretaceous exploration performance.
Westwood also found that Cretaceous targets have accounted for a growing share of global high-impact drilling. Cretaceous plays represented about one-third of wells drilled annually between 2016 and 2020.
“Since 2021, actually more than half of the wells drilled have had Cretaceous targets,” Collard said.
He attributed part of that increase to growing activity along the South Atlantic margins. Similar targets are also being pursued in North America, the Middle East, and the Mediterranean.
Westwood’s analysis showed a difference between the commercial success and resource volumes delivered by the Upper and Lower Cretaceous.
The Upper Cretaceous recorded the stronger commercial success rate. However, Lower Cretaceous discoveries delivered larger overall resource volumes because of their size distribution.
He identified discoveries in Namibia, Côte d’Ivoire, Alaska, Kuwait, and Brazil’s Campos and Santos basins as examples of large Lower Cretaceous successes.
