The drop rates for different qualities of items in Overwatch loot boxes has been revealed by Blizzard Entertainment in compliance with a Chinese law regarding online gaming, in a post on their website (in Chinese).
The law in question was implemented late last year, as detailed by industry analyst Daniel Ahmed (ZhugeEX). In short, it requires that any game that accepts money for randomly received loot must disclose the drop rates for that loot. Randomized digital loot in exchange for real money can be likened to gambling which tends to be heavily regulated. For example, slot machines are required by law in many states (including the Mecca of Gambling, Las Vegas) to return a certain percentage of their take as winnings. Machines and casinos are constantly checked by gaming commissions in order to ensure compliance.
As for Overwatch, the drop rates for loot boxes in China were disclosed in compliance with the new law. Every box is guaranteed to contain at least one item of Rare (blue) quality. On average, a player will receive an Epic (purple) in every 5.5 loot boxes they open. Finally, players will receive one Legendary (orange) item in every 13.5 loot boxes on average.
These probabilities have to be accurate for China to comply with the law, but there's no guarantee that the same probabilities apply for other regions that don't have such a law. Although it might be unusual to do so, there's really no way to tell the drop rates for any game in regions other than China save through experimentation and guesswork. Blizzard Entertainment was one of the first major companies to comply with China's new law regulating randomized gaming rewards.
What do you think of the drop rates for Overwatch's loot boxes? Does it seem fair to you overall, or do you think the chances of getting Epics and Legendaries should be increased a bit? Let us know in the comments below!