The twelfth season of the television series aired in 2008. The twenty episodes were narrated by Michael Angelis in the UK and Michael Brandon in the US.
- Thomas and the Billboard - Diesel obscures Thomas in a photograph of the engines.
- Steady Eddie - Edward takes the Great Waterton water wheel on the scenic route to show off to his friends.
- Rosie's Funfair Special/Rosie's Carnival Special - Rosie and Emily are pulling a train for a fair, but Rosie wants to pull it alone.
- Mountain Marvel - Peter Sam rushes to finish his jobs in order to hear a tale about Proteus from the famous storyteller, Miss Marvel.
- Henry Gets It Wrong - Henry worries that the workmen are going to cut down the wishing tree.
- Heave Ho Thomas! - A large new engine called Hank arrives, but Thomas is determined not to need his help.
- Toby's Special Surprise - Toby wants to make an impression by searching Sodor for something special.
- Excellent Emily - Emily becomes arrogant after receiving praise from the Fat Controller.
- The Party Surprise - Freddie decides to reorganize a winter party from Mr. Percival's house to the Wharf as a surprise for Colin the crane.
- Saved You! - Thomas wants to prove his heroism when he learns a fireman is to be honoured.
- Duncan and the Hot Air Balloon - Mr. Percival's twins are getting a ride in the Hot Air Balloon for their birthday, but Duncan wants to take them himself.
- James Works It Out - When James ignores Hector's advice, he gets caught in bad winter weather.
- Tram Trouble - Toby and Flora are heading a parade at Great Waterton; Thomas thinks Toby would rather lead the event on his own and tries to distract Flora.
- Don't Go Back - Thomas and Diesel race backwards.
- Gordon Takes a Shortcut - Gordon gets lost while taking a shortcut and refuses to ask for help.
- The Man in the Hills - Thomas and the narrow gauge engines collect presents for Mr. Percival's birthday.
- Thomas Puts the Brakes On - Thomas' brakes malfunction while delivering bricks to repair a bridge.
- Percy and the Bandstand - Percy is tasked with bringing Lady Hatt to a surprise party - but the unknowing Lady Hatt tells him to go elsewhere.
- Push Me, Pull You - Skarloey refuses Rheneas' help to pull a train for a puppet show and ends up playing the trucks' games.
- Best Friends - Thomas tries to avoid telling Percy he has been given a job Percy wants to do.
- This was the first season of several things:
- The first season of the CGI Series.
- Sharon Miller's first season as head writer.
- The first season to only have twenty episodes.
- The first season to be produced and filmed in CGI by Nitrogen Studios.
- This was also the last season of several things as well:
- The last season to use models and clay faces, however the clay faces were only used in background shots.
- Simon Spencer's last season as producer.
- The last season to be filmed at Shepperton Studios.
- The last season to feature songs by Ed Welch.
- TV series veteran Steve Asquith's final season.
- This was the last season to have all of the characters voiced by the narrator.
- This was the final season to use the brake sound from The Train.
- This was the last season to have songs sung by children, however the Engine Roll Call would still be used as the intro.
- This was also the only season of several things as well:
- Dino Athanassiou's only season as CGI director.
- Pete Atkin's only season as voice director.
- The only season not to be shown on Japanese TV, but some episodes has been shown exclusively at Thomas Land's 3D Theatre and Video on Demand in Japan.
- The only CGI season not to have a full voice cast for the characters.
- Aside from the Teacher and the tree specialists, all of the characters introduced in this season have only ever appeared in their debut episodes.
- Pierce Brosnan was originally going to narrate this season, but was later replaced by Michael Angelis and Michael Brandon for unknown reasons.
- In the UK, this season was supposed to be shown after The Great Discovery, but was brought forwards for unknown reasons.
- This season was never shown in Norway, Romania, Poland, and the Netherlands.
- Harvey and Arthur were the only engines not to utilize a CGI face mask. However, two pictures from a magazine story show Harvey with a CGI face.
Thomas in the Island of Sodor opening