A great diversity of online dating services currently exists. (See comparison of online dating services.) Some have a broad membership base of diverse users looking for many different types of relationships. Other sites target highly specific demographics based on features like shared interests, location, religion, sexual orientation or relationship type. Online dating services also differ widely in their revenue streams. Some sites are completely free and depend on advertising for revenue. Others utilize the freemium revenue model, offering free registration and use, with optional, paid, premium services. Still others rely solely on paid membership subscriptions.