In the literature, the phenomenon of barrier height lowering in tunneling experiments is mainly assigned to the presence of contaminants at the interface. In this article we present the results of barrier height measurements made between a PtIr tip and various types of gold surfaces. Vacuum deposited and galvanic gold samples are investigated, as received, after ultraviolet (UV)/ozone treatment and covered with a fluid used to lubricate electrical contacts. It is found that the value of the barrier height depends both on the gold deposition process and on the treatment. Results of surface analyses performed on the nonlubricated samples are also reported. They show that the galvanic gold is more contaminated by carbon than the vapor deposited gold. The effects of the ultraviolet (UV)/ozone treatment are then described. It is observed that for nonlubricated surfaces, the higher the oxygen content, the higher the mean barrier height, and that, for each kind of gold, the lubricated surface exhibits the largest barrier height. All these various results are discussed with reference to the results of the surface analyses and to articles found in the literature.