
	March 31, 2026
	(In thousands)
Beginning balance	$	73,141
Additions to capitalized exploratory well costs pending the determination of proved reserves	2,297
Reclassification due to determination of proved reserves	—
Capitalized exploratory well costs charged to expense	—
Ending balance	$	75,438

The following table provides an aging of capitalized exploratory well costs based on the date drilling was completed and the number of projects for which exploratory well costs have been capitalized for more than one year since the completion of drilling:


	March 31, 2026		December 31, 2025
	(In thousands, except project counts)
Exploratory well costs capitalized for a period of one year or less	$	—	$	—
Exploratory well costs capitalized for a period of one to five years	75,438		73,141
Exploratory well costs capitalized for a period of six to ten years	—		—
Ending balance	$	75,438	$	73,141
Number of projects that have exploratory well costs that have been capitalized for a period greater than one year	1		1

As of March 31, 2026, the projects with exploratory well costs capitalized for more than one year since the completion of drilling are related to the Tiberius discovery in Keathley Canyon Block 964 in the Outer Wilcox play in the Gulf of America.

Tiberius Discovery — In July 2023, we spud the Tiberius infrastructure-led exploration prospect located in Block 964 of Keathley Canyon in the Gulf of America, which encountered hydrocarbon pay. Initial fluid and core analysis supports the production potential of the well, with characteristics analogous with similar nearby discoveries in the Wilcox trend. In March 2024, we completed the acquisition of an additional 16.7% participating interest in the Keathley Canyon Blocks 920 and 964, offshore Gulf of America. As a result of the transaction, Kosmos’ participating interest in the Tiberius discovery area increased from 33.3% to 50.0%. The Tiberius project is being progressed as a phased development with a final investment decision for the development achieved in March 2026.