Offshore structures are often founded on mud-mat foundations which prevent the structure from settling excessively. Pressure differences are generated under mud-mats during removal from the seabed. These differences lead to a force that resists the uplift. A literature study on breakout resulted in a hypothesized distinction of four mechanisms that occur during the uplift of offshore shallow foundations. An experimental program was designed to study these mechanisms. Small-scale tests on clay and sand were executed. The effectiveness of selected mitigation measures was studied, as well as the influence of the measures on the mechanisms. Existing calculation methods that model suction or quantify the breakout force were evaluated. It is believed that the results from the experimental program led to a comprehensive list of parameters that should be included in a design method to model the total resisting force to uplift, taking the mechanisms into account.