In queue mode, observations defined by the investigators are carried out on their behalf by the Gemini scientific staff. Several factors combine to determine which observation is executed from the pool of possible observations but predominant are scientific ranking and the closeness of match to the current observing conditions. There are no maximum or minimum time limits for single observations, but long observations are likely to be split in order to be integrated into the nightly plan (see each instrument's overheads page for details).

Each queue observation must be defined in detail, including telescope and instrument configurations and sequences (e.g. telescope and guide star coordinates, grating and slit settings, dither, chop and nod patterns). The detailed definition of observations is undertaken in Phase II of the proposal process using the Observing Tool (OT).

Scheduling restrictions, or observing condition constraints, fall into four categories which must be specified by the investigator for each observation (or globally for groups of observations up to and including the entire program) and define the poorest conditions under which the observation can be executed. These constraints are image quality, sky background, sky transparency, and cloud cover. Some of these properties have wavelength dependence. Care should be taken in selecting appropriate conditions; the observing condition constraints page contains detailed information that may be useful, including atmospheric transmission and emission spectra. The scientific demands of the particular program, the characteristics of each constraint, and the likelihood of their combined occurrence should drive this choice. Certain instruments may have additional scheduling restrictions, which are detailed along with the Call for Proposals.

The description of telescope coordinates, instrument configurations and scheduling constraints, which form part of Phase I and are necessary to demonstrate technical feasibility, has been separated from the detailed observation definition which takes place in Phase II. Technical support for investigators prior to the submission of completed Phase II information to Gemini Observatory is provided by the partner National Gemini Offices (NGOs). Upon submission of the completed Phase II program, the assigned Gemini Contact Scientist (CS) becomes the first point of contact for all subsequent queries.

Modification of approved queue programs must be made via the change request process.

The Gemini Science and Technology Advisory Committee approved a remote eavesdropping observing mode for queue programs, which started in Semester 2013A following a trial late in 2012B.