Conversation so far:
who was rockefeller's business partnership with?
In 1859, Rockefeller went into the produce commission business with a partner, Maurice B.
Clark, and they raised $4,000 ($108,948 in 2017 dollars) in capital.
what kind of busiiness were they into?
In this environment of wasteful boom, the partners switched from foodstuffs to oil, building an oil refinery in 1863 in "The Flats".
what other partnership did he have?
The commercial oil business was then in its infancy.
Whale oil had become too expensive for the masses, and a cheaper, general-purpose lighting fuel was needed.
what else can you tell me that is interesting?
Rockefeller bought out the Clark brothers for $72,500 (equivalent to $1 million in 2017 dollars) at auction and established the firm of Rockefeller & Andrews.
what did the firm do?
He was well positioned to take advantage of postwar prosperity and the great expansion westward fostered by the growth of railroads and an oil-fueled economy.
when did they buy out the clark brothers?
In February 1865.
what else did they do about oil?
He borrowed heavily, reinvested profits, adapted rapidly to changing markets, and fielded observers to track the quickly expanding industry.

Question: what did they use when whale oil got too expensive?
Self-contained rewrite: What did Rockefeller use when whale oil got too expensive?