Hi, They are very often interchangeable with no difference in meaning. However, there are times when one is clearly more preferable than the other. 'I'm thinking of a reason not to go to the party.' (not 'about') and 'I'm thinking about why I like Europe so much.' (not 'of') The difference is subtle and seems to me to be like this: 'thinking of' - a thought has come to mind 'thinking about' - you are giving more time to the thought e.g. I thought of a reason not to go the party and now I'm thinking about the consequences. Hope that helps!

Hi! In fact I think there is no difference between the both!!