American Airlines flights from New York JFK to Barcelona, Spain are priced at $376 to $423 round trip for nonstop travel January 26 to May 26, 2017. But lowest prices for dates I checked are tickets purchased through Oneworld partners British Airways, Finnair or Iberia for AA-operated flights, while American is charging $38 to $52 more on its own website for the same nonstop flights.
British Airways ticket for American Airlines-operated nonstop flights
New York JFK – Barcelona, Spain BCN
American Airlines ticket for same New York JFK – Barcelona, Spain BCN nonstop flights