Houston oil field services firm Keane Group is boosting its hydraulic fracturing power, buying Denver fracking company RockPile Energy Services for about $285 million in cash and stock.

RockPile owns eight wireline trucks, 12 workover rigs, 10 cement units and 245,000 horsepower in frac pumps. Its equipment is 100 percent deployed, in North Dakota’s Bakken and West Texas’ Permian oil fields.

The addition will increase the size of Keane’s fleet, already one of the largest fracking fleets in the U.S., by one-quarter, it said.

The purchase includes Keane paying about $26.5 million for previously ordered hydraulic fracturing equipment. Keane expects to deploy the new horsepower to the Bakken, which stretches from North Dakota to Canada, in the fourth quarter.

Keane is taking out $135 million in term loans to fund the purchase. It expects to close by July 31.