Ten artificial tracers were tested in lab experiments as tool to quantify contamination of deep ground water samples by drilling fluid. The tracer batch experiments ordered by Nagra were conducted with a defined starting concentration of each tracer in four different drilling fluids (Polymer-, Pure-Bore®-, Potassium Silicate-Drilling Fluid and High Performance Water-Based Mud) in regard to recovery rate (0, 3, 5, 101 days) and in powdered Opalinus Clay (OC) suspensions (10, 20, 50 g ad 100 ml demin. water) in order to simulate the uptake by solids in the drilling fluid. The recovery rate was measured at the beginning, after 1 day, 9, 29 and 58 days. The tracers were analyzed by HPLC-FLD using silica columns or a graphite column depending on the used tracer. For the choice of tracer, the following properties must be considered: heat stability, sorption affinity and solubility. We found out that Uranine (UR), Sodium-Naphtionate (NaN), 1-Naphtalene- (1NSA), 1,5-Naphtalene di-sulfonic acid (15NDSA), Pyranine (PYR) and Sulforhodamine G (SRG) are favored for the tested drilling fluids. UR was stable during longterm studies (101 days), has a good recovery rate and a high detection sensitivity. Further, UR, NaN, 1NSA und 15NDSA have shown low sorption. 1NSA and 15NDSA have a good heat stability but a high detection limit. We found out that NaN is suitable for all tested drilling fluids due to its good solubility, high light stability, low sorption affinity and selective detectability. Eosin Y (EOY) is not recommended because of sorption and light sensitivity and 1,3,6-Naphtalene trisulfonic acid (136NTSA) showed little sorption affinity and might only be applicable at high concentrations (> 10 mg/L). 1,3,6,8-Pyrene tetrasulfonic acid (1368PTSA) concentrations were measured near the detection limit. Maybe this tracer would be useful in higher concentrations (100 µg/L). The pyrene derivates PYR and 1368PTSA are not recommended due to strong sorption to the tested drilling fluids. Sulforhodamine B (SRB) showed low recovery rates between 88 % and 95 % which might be caused by high sorption affinity. The results from the lab experiments using suspensions of OC show that the system OC-Water is very complex for determination of the concentration of added tracer. In general, the variance of recovery rate is increasing with higher solid to liquid ratios of the OC suspensions. However, we found out that 15NDSA, 1NSA, UR and limited NaN (high detection limit) are favored tracers for the use in boreholes with OC. 15NDSA seems to be the most useful tracer for high concentrations of OC maybe up to 200 g/L also over a longer period of time. 1NSA, NaN and maybe UR can be used for low OC concentrations (100 g/L) for short term experiments. In the suspensions of a high solid to liquid ratio more or less all tracers were adsorbed on the OC. For this experiments 15NDSA showed the best recovery rate of 43 % after 58 days. In practice, however, the detection limit of UR by fluorescence spectrometry is significantly lower compared to the other tracers, allowing a reliable monitoring of the tracer concentration at the drill site. The tracers showing a higher stability in the presence of OC may be added for specific drilling sections, increasing the reliability of the determination in the laboratory of ground- or porewater sample contamination.