Space Quest I: Roger Wilco in the Sarien Encounter

The game was programmed using Sierra's AGI engine and featured a pseudo-3D environment, allowing the character to move in front of and behind background objects. The primary means of input in Space Quest, as in many other AGI games, was through the use of a text parser for entering commands and use of the keypad or arrow keys for moving Roger Wilco around the screen. The Amiga, Apple IIGS, Atari ST and Mac versions of the game offered basic mouse support for movement as well. The game had a 160×200 resolution displaying 16 colors. Sound cards were not available in 1986, so sound was played through the PC's internal speaker; owners of Tandy 1000, PCjr and Amiga computers would hear a three-voice soundtrack, while Apple IIGS owners were treated to a fifteen-voice soundtrack with notably richer sound.

A precursor of this game is the interactive fiction game Planetfall, created by Infocom, whose player-character is a lowly "Ensign Seventh Class" who does the lowest form of labor aboard a spaceship and who appears on the cover with a mop. Just as King's Quest adapted the text-adventure puzzle games set in a medieval world to a visual display, Space Quest did the same for the space puzzle game.

As a form of copy protection, coordinates in the game while in the escape pod as well as the rocket purchased at Tiny's Used Spaceships are only found in the manual. Also, the code for retrieving the cartridge aboard the Deltaur can only be found in the manual.

In addition to this, the AGI version had key disk protection where the user was required to insert the original game floppy on startup.

Sierra released three versions of Space Quest: the original 1986 AGI V2 release, the 1987 AGI V3 release, and the 1990 VGA release. Aside from minor sound/graphics differences, the PC, Amiga, Atari ST, and Apple IIgs versions are largely identical. The Mac version is considerably different due to being monochrome and completely menu-driven. In addition, Space Quest had an 8-bit Apple II version for the //e and IIc. This had no pull down menus and displayed all text at the bottom of the screen.

Along with King's Quest III, Space Quest was the first Sierra game to feature pull down menus, be hard disk installable, and not require a specially formatted save disk (except the Apple II version as noted above).