Defying oil-price jitters, Quantum Energy Partners collected about $2.6 billion from investors to cast new wagers on hydrocarbon-rich regions, said people familiar with the matter.

Quantum is seeking as much as $5.25 billion for its latest fundraising effort, the people said. This month’s first closing for the new fund, Quantum Energy Partners VII LP, comes as the firm has struck a quick succession of energy-patch deals.