Delta Air Lines announced it is adding to its in-flight entertainment options on some of its aircraft, including more shopping and entertainment on its free in-flight wi-fi portal, as well as on-demand movies and television through wi-fi.

For those with wi-fi-enabled devices, Delta is adding to its free in-flight portal called called Delta Connect. It now offers more free shopping and entertainment, along with flight information, which do not require a payment for in-flight wi-fi service.

And on flights on Delta's 16 Boeing 757-300 jets, travelers with laptops can buy on-demand movies for $3.99 and up, and on-demand television at an introductory price of 99 cents, which will not require a separate payment for in-flight wi-fi. Travelers will be able to play back the movies and television shows on the same device for at least 24 hours after their flight. Delta said it will expand the on-demand offering in early 2012 to tablets and mobile devices on the 757-300s, which have overhead screens but do not have seat-back entertainment systems.

Atlanta-based Delta is installing wi-fi on many of its domestic aircraft, including some of its regional jets, and expects to soon have in-flight wi-fi on more than 800 of its planes. The in-flight entertainment additions are part of a broader $2 billion investment by Delta to improve the experience for customers.