Verse number 89 of Sura al-M'idah has clearly legislated the compensation for a broken oath.
"The atonement for it is to feed ten needy persons with the average food you give to your families, or their clothing, or the freeing of a slave. He who cannot afford] any of these [shall fast for three days. That is the atonement for your oaths when you vow. But keep your oaths. Thus does Allah clarify His signs for you so that you may give thanks." (5: 89)
According o this verse, the compensation of an oath in our time would be to feed ten poor individuals or provide clothing for them. In case this is not affordable, he person must fast for three consecutive days.