After a surprising cut by OPEC and allies, European markets end the day lower, while oil and gas stocks rise by 4 percent.

Monday's slight decline across Europe's stock markets came as investors focused on the oil market in the wake of a surprise production cut by the OPEC+ alliance.

After being flat for most of the afternoon, the pan-European Stoxx 600 index ended up 0.1%.

Brent crude futures and U.S. West Texas Intermediate crude futures both increased, which led to a 4 percent gain in the oil and gas industry. This comes after OPEC a....