Hi. I'm surprised about this myself: since I started learning English, I've never been sure how to form the 's-genitive with words that end in s or ss. Is it correct to write: Jonas's car, Jess's car or should I write Jonas' car, Jess' car or maybe even something completely different? In case I should write Jonas's, how should I pronounce that? [Jonas] or [Jonases]? Jonas' would just be [Jonas], I imagine. I'm looking forward to your answers.