According to the British Egg Information Service, one in every thousand eggs on average is a double-yolker. They're not sure how they've come to this figure but you would like to think that the British Egg Information Service was able to supply useful information about British Eggs, so let's give them the benefit of the doubt.
So, if the probability of finding an egg with two yolks is 1/1000 - then to find the likelihood of discovering four in a row you simply multiply the probabilities together four times. One thousand to the power of four brings us to the grand total of one trillion - that's the new-school US-style trillion with 12 zeroes.
If true that would mean the event that occurred in Jen's kitchen was a trillion-to-one event. But is it true? No is the short answer.
Many factors can affect these odds, like the possibility that a certain chicken or flock laying several eggs that ended up in one carton, or the sorting of eggs by size. There are other factors as well, explained in this BBC article. Link -via Metafilter