Travel by air or sea with ESTA must be made on a participating commercial carrier. ESTA is not needed when entering the United States by land, but the VWP does not apply at all if arriving by air or sea on an unapproved carrier (e.g. a private ship or plane), in which case a standard visa is required. As of December 2018, ESTA is no longer approved in real-time and passengers are required to apply at least 72 hours before departure.