Adding to [David Cash's answer](https://crypto.stackexchange.com/questions/5385/why-does-oaep-have-2-rounds-with-2-random-oracles/5394#5394), besides SAEP and SAEP+ by Boneh, there is another paper that improves OAEP using only a one-round Feistel structure and has an additional feature: redundancy-free encryption (which none of OAEP, SAEP and SAEP+ have). Read [Verified Security of Redundancy-Free Encryption from Rabin and RSA](https://eprint.iacr.org/2012/308.pdf) by Barthe, Poitcheval and Beguelin (2012).