The Options Clearing Corporation is the entity that manages options adjustments for situations like this. Article VI, Section 11 of their by-laws describe the situations and possible adjustments. They put out an informemo for each adjustment that explains the adjustment. Infomemo 31854 was issued for Abbott on Dec 12. Effective Jan 2, 2013 the option symbol changes from ABT to ABT1, no change to strike prices, no change to the number of contracts, the multiplier remains 100, the new deliverable per contract is 100 ABT common shares and 100 ABBV common shares, the settlement allocation is ABT: 50% and ABBV: 50%. The strike price remains 60 and when you exercise you will receive 100 shares of each company for each contract.