Bagci, S. and Gumrah, F., 1992. An examination of steam-injection processes in horizontal and vertical wells for heavy-oil recovery. J. Pet. Sci. Eng., 8: 59-72. This study presents an experimental investigation of heavy-oil recovery by steam injection in a three-dimensional modal containing 17 degrees API crude oil. The first part of this paper describes the experimental apparatus. Emphasis in this paper is on the effect of the combination of horizontal and vertical wells on steam-injection efficiency. Four cyclic steam-injecticn experiments were conducted. Two used a vertical well at the center of the model, and two used a horizontal well scheme showing better oil recovery and steam/oil ratios than the vertical well scheme. Soak time as well as the amount of steam injected per cycle were investigated. For both schemes, small slug sizes seem to give initially better steam/oil ratios than expected, however, cumulative oil recovery for vertical wells do not depend on slug size, while for horizontal wells, small slugs followed by larger slugs gave a better recovery by 8% of the original oil-in-place (OOIP), compared with large slugs followed by smaller ones.