In the Book of Kings, it says that Omri became king of Israel in the 31st year of Asa and ruled for 12 years, but it then says that Ahab, the son of Omri became king of Israel in the 38th year of Asa, which is only 6-7 years after Omri became king.
So, there is a discrepancy. I do not think this discrepancy can be arguing that there was a co-regency for two reasons. First of all, there is no mention of a co-regency and the general context of the Book of Kings is such that a shared throne would be worthy of mention. Also, the text specifically says that Omri died and was buried in Samaria, and his son became king in his stead (autou ant autou). Since the text specifically says that he succeeded him, it cannot be a co-regency.
Now, the Septuagint seems to say something different, that Ahab became king during the reign of Jesophat, son of Asa, not during Asa's reign. If so, why would the Masoretic text say that he became king in the 38th year of Asa?