Piper Jaffray Cos. (NYSE: PJC) is acquiring energy-focused investment bank Simmons & Co. International for $139 million in order to expand services in an area where dealmakers expect to see more M&A.

The firm's latest  target, Simmons, provides M&A advisory, capital markets execution and investment research throughout the entire energy spectrum, including energy services, equipment, exploration, production, midstream and downstream. The Houston-based firm, founded in 1974, has executed more than 830 strategic advisory deals and 330 private and public financings valued at about $260 billion.

Some of the transactions Simmons has recently advised on include USD Partners LP's (NYSE: USDP) $225 million agreement to buy Casper Crude to Rail LLC, and Pilot Thomas Logistics' deal for a majority stake in Economy Boat Store, which sells diesel fuel, lube oil and other supplies.

"This addition represents a major step in our drive towards $500 million in annual investment banking revenue," says Piper Jaffray CEO Andrew Duff.

Minneapolis-based Piper Jaffray was named Mergers & Acquisitions M&A Mid-Market Investment Bank of the Year for 2014, in part because of previous acquisitions the firm made. Back in 2013, the firm picked up Edgeview Capital Partners LP and Partnership Capital Growth – its first ever investment banking purchases. Earlier in 2015, the firm agreed to buy BMO Capital Markets GKST Inc., a municipal bond sales, trading and origination business.

"Expanding into the energy sector has been a long-term goal for us," says Scott LaRue, global co-head of Piper Jaffray investment banking. Dealmakers are expecting more M&A activity in the energy sector, according to the results of Mergers & Acquisitions Mid-Market Pulse.

The purchase price breaks down into $91 million in cash and $48 million in restricted stock. Piper Jaffray has also committed $21 million in cash and stock for retention purposes. Simmons generated $96 million in revenue for the fiscal year ended June 30, including $65 million in advisory revenue.

There have been quite a few deals involving middle-market investment banks recently.

Also on Nov. 17, Houlihan Lokey (NYSE: HLI) picked up the investment banking operations of Leonardo & Co. NV, in Germany, the Netherlands and Spain. Leonardo provides financial advisory and restructuring services in Europe, and the deal expands Houlihan's global footprint. The firm has made a handful of acquisitions recently, including McQueen Ltd., a London-based consumer advisory business, and Bridge Strategy Group, an operations consulting firm.

Earlier in November, investment bank Stifel Financial Corp. (NYSE: SF) announced it was buying Eaton Partners in order to expand relationships with hedge funds, private equity firms and high-net-worth family offices. Before that, Regions Financial Corp. (NYSE: RF) announced a plan to buy BlackArch Partners, a Charlotte, North Carolina-based middle-market investment bank.