Generally speaking, most contacts can be either written or oral and legally enforceable, however there are several types of agreements which have to be in writing. I listed them below.
1. Real estate sales
2. Agreements to pay someone else’s debts
3. Contracts that take longer than one year to complete
4. Real estate leases for longer than one year
5. Contracts for over a certain amount of money (depending on the state);
6. Contracts that will last longer than the life of the party performing the contract
7. A transfer of property at the death of the party performing the contract.

The reason why these agreements can not be oral agreements is that oral contacts are very difficult to enforce since there’s no clear record of offer,consideration and acceptance .