To be able to play songs in any key spontaneously is a great skill to acquire. This is especially useful when one of your 'audience' wanted to sing a certain song or when you're jamming in a group.

However, whenever there is a request to play a song, I normally would use the C, F or G major scale and the related chords to start with. This is because I am familiar with the chords harmony and able to fit them in nicely with the melody (Eg. when to use Fm on G bass, Dm-5 on A flat bass etc.). I will try to use the original key of the requested song if I am familiar or had played it before.

Although I could play a song in other keys, often I had to pause in between to get the right chords to fit in and not as spontaneous as using C, F or G keys. I have friends who could use E flat, A flat etc spontaneously.

I curious to know how many keys do you all master under your fingers? Or, what are the common / must-know keys to be able to cover any song requests?