How many expiations are incumbent upon one who has broken his oath twice consecutively regarding not masturbating?

Swearing to abandon a sin makes it obligatory to fulfill the oath and prohibits breaking it. Sincere repentance from the sin and from breaking the oath is obligatory. In your case, you owe two expiations for breaking the oath on the two occasions you swore, and this is the view of the majority of scholars. The expiation for an oath is feeding ten poor people, or clothing them, or freeing a slave; and if one cannot find these, then fasting for three days.