The energy sector enjoyed a broad, and in many cases sharp, rally in afternoon trading Monday, as crude oil prices rose to a 3-month high on increasing hopes that a potential COVID-19 vaccine would fuel and economic recovery and spark demand for oil. The SPDR Energy Select Sector exchange-traded fund /zigman2/quotes/206420077/composite XLE -2.96% ran up 5.8%, toward the highest close since Aug. 17, with all 25 of its equity components trading higher. The ETF was biggest gainer of the 11 SPDR sector ETFs tracking the S&P 500's /zigman2/quotes/210599714/realtime SPX -1.31% 11 key sectors. The biggest gainers were Occidental Petroleum Corp.'s stock /zigman2/quotes/207018272/composite OXY -0.82% , which soared 15.5%, and Diamondback Energy Inc.'s stock /zigman2/quotes/201200230/composite FANG -0.82% , which shot up 10.8%. Crude oil futures /zigman2/quotes/209723049/delayed CL00 -0.20% climbed 1.5% to $43.05, toward the highest close since Aug. 26. Among other more-active stocks in the energy ETF, shares of Marathon Oil Corp. /zigman2/quotes/205031829/composite MRO -2.48% hiked up 6.6%, Exxon Mobil Corp. /zigman2/quotes/204455864/composite XOM -2.56% advabced 5.4%, Kinder Morgan Inc. /zigman2/quotes/208455654/composite KMI -3.55% climbed 2.8% and Halliburton Co. /zigman2/quotes/210488727/composite HAL -3.21% hiked up 9.0%. In comparison, the S&P 500 /zigman2/quotes/210599714/realtime SPX -1.31% tacked on 0.4%.