(57) A process is provided for the recovery from petroleum- bearing formations of ultra-heavy crudes and tars. A 'daisy' well is employed with a main central bore surrounded by an array of slant bores. Hydrogen donor solvent is injected under prssure into the formation via the central bore and high temperature flue gases are injected at higher pressure via the slant bores. Dissolved and liquefied hydrocarbons are recovered together with solvent by gas lift in the central bore. The recovered hydrocarbons are reformed by a thermochemical reforming plant adjacent the well-head to obtain a pipe-line quality product. The plant includes a high temperature high pressure furnace from the exhaust of which the hot flue gases are obtained, and output fractionation stages from which the solvent is recovered.