Should I use Singular or Plural name convention for REST resources?

Some RESTful services use different resource URIs for update/get/delete and Create. Such as

• Create - using /resources with POST method (observe plural) at some places using /resource (singular)
• Update - using /resource/123 with PUT method
• Get - Using /resource/123 with GET method

I'm little bit confused about this URI naming convention. Should we use plural or singular for resource creation? What should be the criteria while deciding that?