At the foot of the giant Hebes Mensa salt dome on Mars, there is a feature called the "Oil Spill" (Adams et al., 2009). But, ccording to Adams et al., it consists of liquid brines that have been coloured black by dark dust particles. However, - this is not be true.
Figure 1. This is what the "Oil spill" feature looks like on Google Mars.
To me, this explanation is not probable. According to own earth-bound research, over the past 5 years, the most plausible and probable explanation is thatthe liquid substance consists of crude oil.
Read the full explanation for why this is crude oil leaking out of Hebes Mensa at my blogsite: www.oilonmars.blogspot.no