London—Oil prices rose on Friday, heading towards a sixth consecutive weekly gain, as geopolitical tensions continue to raise supply concerns. Brent crude futures were up 66 cents, or 0.7 percent, at $90 a barrel by 1225 GMT, having hit $91.04 on Thursday for their highest since October 2014. U.S. West Texas Intermediate (WTI) crude futures rose 57 cents, or 0.7 percent, to $87.18. WTI also reached a seven-year high of $88.54 earlier in the session. Both Brent and WTI are on track for what would be the longest run of weekly gains since October. Supply scarcity has pushed the six-month market structure for Brent into steep backwardation of $6.56 a barrel, the widest since 2013. This means that current levels are higher than those in later months, which usually encourages traders to release oil from storage to sell it promptly. Oil prices continue to receive support from concerns that the …