Energy stocks fell late Monday afternoon, with the NYSE Energy Sector Index and the Energy Select Sector SPDR Fund (XLE) each declining 1.6%.

The Philadelphia Oil Service Sector index shed 2%, and the Dow Jones US Utilities index fell 0.2%.

West Texas Intermediate crude oil declined 2.1% to $57.09 a barrel, and global benchmark Brent dropped 1.8% to $60.22 a barrel. Henry Hub natural gas futures fell 1.3% to $3.58 per 1 million BTU.

In corporate news, NGL Energy Partners (NGL) shares rose 3.7% after the company said it raised $270 million from noncore asset sales, including 17 natural gas liquids terminals and the Green Bay terminal in Wisconsin.

Portland General Electric (POR) shares rose 1.6% after UBS Securities upgraded its rating to buy from neutral.

Sunoco (SUN) agreed to buy Canada-based Parkland in a cash-and-equity deal worth about $9.1 billion, including debt, the companies said in separate statements Monday. Sunoco shares were falling 5.9%.

Shell (SHEL) has been discussing with advisers in recent weeks to assess a potential acquisition of BP (BP), Bloomberg reported Sunday. Shell shares were down 2.2%, while BP gained 3.4%.