Contracts take many, many forms. A contract can be made up of oral terms, written terms, or a blend of both. Each is enforceable and each has its risks.
Oral contracts are the most precarious. Frankly, human memories are horrific. Secondly, while the most prominent terms (usually what is being paid and the primary good or service being delivered) are remembered, the important details will either be forgotten, memories will disagree on what was agreed to, or the conversation will stray and important details will not even be discussed.
A blended oral and written contract is one where there is an oral agreement supplemented or memorialized by a summation writing. This is more comforting as there is some document that can be pointed to for affirmation of agreed to terms. With the shortcomings of human memories, contemporaneous writings constitute superior evidence. The peril with this form of a contract is that not all terms get captured, even if the terms were discussed and agreed to by the parties.
From a lawyer's perspective, the most preferred form of a contract is a fully written contract signed by the parties. Do not feel the distance between parties excuses written contracts; it is so easy to send a scanned agreement from Hugo to St. Cloud for essentially immediate signing or recognition by the parties. It also gives everyone a chance to see the terms and think about what the terms actually mean -- words have a different connotation in the context of a written agreement compared to their usage in a conversation.
From a practical perspective, I get it that oral agreements happen all the time and commonly work just great. But, if you ever get a sense that the other side is just a little slippery, trust your instincts and call me. Spending a few hundred dollars up front could save your deal and save you tens of thousands of dollars down the road.