BA Gold:
Here are the exact rules as taken directly from Sabre:
2 ADDITIONAL FLT SEGMENTS WITHIN EACH
CONTINENT - EXCEPT CONTINENT OF ORIGIN-
MAY BE PURCHASED AT A CHARGE PER
SEGMENT OF:
FIRST - USD550/AUD750/GBP350/
HKD4300/EUR450.
BUSINESS - USD400/AUD500/GBP200
HKD3200/EUR300.
ECONOMY - USD150/AUD200/GBP75/
HKD1200/EUR100.
FLT SEGS BEYOND THE NUMBER PERMITTED
AT THE THROUGH FARE MAY BE PURCHASED
IN THE SAME OR LOWER CLASS OF SERVICE
THAN THAT OF THE OW EXPLORER.
Since you have an F class OWE...you can buy either F, C or Y as the additional segments.