Is a return ticket really necessary when travelling south america?

I'm soon going to South America, and my trip starts in Venezuela. Now my understanding is that as a Maltese citizen i don't require any Visa, however it seems as though a return/onward ticket is required. Since i will be traveling around South America for around a year, and i don't know what route im taking, purchasing a return ticket doesn't really make sense to me... Does anybody know, from their own experience whether this will really be a problem? Thanks :)