Investors increased their bearish bets in the energy sector in the past month, as a decline in crude oil prices led to broad weakness in the sector. Based on the most recent exchange data, the median industry short interest, or bets that the shares would fall, was approximately 4% of the shares outstanding as of Dec. 15, up from about 3% a month, according to MKM Partners analyst John Gerdes. The increase in shorts occurred as the SPDR Energy Select Sector ETF /zigman2/quotes/206420077/composite XLE -0.85% declined 5.0% and crude oil futures /zigman2/quotes/209723049/delayed CL00 -1.61% tumbled 12.4% in the month to Dec. 15, while the S&P 500 /zigman2/quotes/210599714/realtime SPX -0.59% gained 0.6% over the same time. Of the companies Gerdes covers, he said the stocks with the highest short interest as a percent of shares outstanding, each at 13%, were Callon Petroleum Co. /zigman2/quotes/201917664/composite CPE -2.62% , CNX Resources Corp. /zigman2/quotes/208647486/composite CNX +0.67% and Laredo Petroleum Inc. . The others with double-digit short-interest percentages, each at 11%, were Centennial Resource Development Inc. , Chesapeake Energy Corp. /zigman2/quotes/224537584/composite CHK -1.24% and Magnolia Oil & Gas Corp. /zigman2/quotes/200885355/composite MGY -1.38% .