All three alliances have SFO to London on sale for $670 to $700 on their own websites for travel from January into summer and fall months 2017. Even better is the availability of online travel agency fares in the $550s for summer travel.
Oneworld Alliance has San Francisco to Rome at $666 round trip on British Airways website, even in July 2017. Like the London fares, this ticket is also available in the $550s for summer travel with online travel agencies.
Momondo.com and Skyscanner.com pull up these big discounts on $670 to $700 fares.
FlightsMojo.com ticket Virgin Atlantic flights
Los Angeles LAX – London LHR / London LGW – Las Vegas LAS – LAX
TravelMerry.com ticket Lufthansa and United flights.
San Francisco SFO – London LHR / London LGW – Toronto YYZ – San Francisco
$618.26 round trip Tue July 18 – Fri July 28 (mid-August fares drop to $552.)
$552 Rome, Italy in July
Kiss&Fly.com ticket for British Airways codeshare American Airlines operated flights
San Francisco SFO – Philadelphia PHL – Rome FCO – Philadelphia PHL – SFO
$552.71 round trip Wed July 5 – Wed July 12 (Google Flights link to AA $666 fare)