Former Sonic & SEGA artist Satoshi Okano has recently uncovered some of his hold sketchbooks and has been posting the content to his Twitter account. In addition to the Speed Highway Spider Girl, which we already reported on here, he's also been posting loads of other never-before-seen Sonic concept art.
He's posted a lot, so let's go through it!
First, we have some Sonic Jam concept art, specifically for the buildings from Sonic World, the game's 3D museum hub.
Next, we have some Mystic Ruins concept art, alongside some SEGA Saturn Magazine cover concepts:
Most of the rest of Okano's art is connected to Dr. Eggman and the Egg Carrier. Here, we have concept art for Eggman's pool, a water tank, and a Sonic Nike shoe concept Okano drew for himself:
We have more art from the Egg Carrier, including the room where Gamma gets his booster upgrade, the place where Eggman delivers his speech to the E-100 units, concepts for the Egg Carrier's Tram service and cannons, two pages of concept art devoted to Eggman's room (apparently he's got cigars?), and finally a page of other random Eggman related concepts, and "unasked for" character art.
Fly the Bat isn't actually Sonic related. He's based off a character Satoshi Okano created for the SNES game "Uchuu Racer: Astro Go! Go!". It seems Okano just drew some art reimagining him as a Sonic character. On that note, here's the most complex piece of art Okano has posted with the character, which he called "Unreliable Stage."
Finally, Okano has also posted some concept art from Samba de Amigo:
This might not be the last of Okano's Sonic work, so be sure to stay tuned (and give Satoshi Okano a follow)!