Welding is an extensively used technology by different industries such as aerospace, automotive and marine industry. Welding involves the temporal melting of materials in order to join them together. The quality of the weld is known to depend on the fluid flow and heat transfer in the material. A way to influence the heat transfer and fluid flow, and thus the quality of the weld, is by using different power-density distributions. However, the current literature falls short when combining the different power-density distributions with weld pool behaviour. The aim of this thesis is to study the effects of laser power-density distribution on heat and fluid flow in molten metal melting pools. This will be done by running weld pool simulations using a 2D axisymmetric, flat surface model. These simulations use a top-hat, Gaussian or doughnut laser power-density distribution. Besides, the cases have been simulated for a 20 ppm and a 150 ppm sulfur concentration. That the sulfur concentration has an influence on the weld pool shape was already shown in previous studies. However, it was not known how much the influence of sulfur concentrations varied for different laser power-density distributions. The laser power-density distributions are found to have a significant influence on the weld pool shape. The doughnut power-density distribution created a three times deeper weld pool than the Gaussian and top-hat power-density distribution. The maximum temperature of the weld pool was also influenced by the power-density distribution. In the case with a sulfur concentration of 20 ppm a discrepancy of 1000 K has been found between the Gaussian and doughnut distribution. The influence of sulfur concentrations varied for different laser power-density distributions. This influence of the sulfur concentrations has been measured through the difference in aspect ratio for different sulfur concentration cases. For both the top-hat and Gaussian power-density distribution, the aspect ratio differed 0.02 when using a 20 ppm versus a 150 ppm sulfur concentrations. The doughnut power-density distribution reached a higher difference in aspect ratio of 0.1 when using a 20 ppm versus a 150 ppm sulfur concentrations. The use of different power-density distributions in weld pool simulations results in different weld pool behaviour. Besides, the combination of different sulfur concentrations with power-density distributions largely influenced shape, temperature and fluid flow of the weld pool, which results in a great variation of weld pool shapes and sizes. Because there are different requirements for different welding cases, these results are useful in order to construct a quality weld.