Fare alert that United, Lufthansa, Air Canada and Star Alliance airlines have ticket prices down to $390 round trip San Francisco to Barcelona on their airline websites for travel mid-August to February 2018. These prices are even lower, down to $308 round trip through online travel agencies.
Lufthansa Airlines San Francisco SFO – Frankfurt FRA – Barcelona BCN – Washington IAD – San Francisco SFO
United Airlines San Francisco SFO – Washington IAD – Barcelona BCN – Montreal YUL – San Francisco SFO
TravelMerry.com ota ticket for Air Canada operated flights ticketed as United Airlines codeshare flights
San Francisco SFO – Los Angeles LAX – Montreal YUL – Barcelona BCN – Toronto YYZ – San Francisco SFO