Open Access Same-Time Information System

OASIS is the web-based trading system for electrical power transmission service in North America.

The "Open Access" policy for transmission service in the United States was created by Federal Energy Regulatory Commission Order 888, and the OASIS system to support it by Order 889, both issued April 24, 1996. US power line owners were compelled by Order 888 to open their power lines to competitive use, while reciprocity agreements extended this competitive market for transmission service into jurisdictions in Canada and Mexico.

The capacity to carry electricity on each power line is a limited resource. These resources are managed by reservations for a specified power level to flow over high-voltage power lines along a market path for a given duration. Physically, power travels according to the laws of electricity on multiple power lines, so the power system is cooperatively regulated to make the correct amount of power appear at each point in the market path, while respecting the capacity limit of individual power lines.

OASIS nodes are operated by transmission providers. Transmission customers access these nodes on the internet to create reservations. A long-distance power transaction may require multiple transmission reservations to get the power from the source to the destination.