As Gareth said, the subjunctive "were" is preferred (as being more correct and more precise) in formal writing. But "was" is much more common in daily speech. "I wish I was rich" sounds a just a little uneducated to me, but only because I read a lot. But to most people (in the US) it sounds perfect. (On the other hand, don't confuse this usage with the past tense "there were three people at the beach". You will sometimes hear from very badly educated people the following: "There was three people at the beach"..... this is bad BAD incorrect.) Good luck

Take a look: - https://en.oxforddictionaries.com/grammar/when-to-use-the-subjunctive A snippet: > Usage seems to be changing in phrases such as if I were you, if it were up to me, etc. People often say if I was you and if it was up to me, but the subjunctive is preferable in writing, especially any formal or academic prose. Hope that helps.