The planning of least-cost investments in energy sector continues to be important issue for the utilities, consumers and the whole society. The contemporary planning methods are based on special mathematic models. Some of these programmes are used in Latvia (WASP, UPLAN, MESSAGE, MARKAL). These tools are very effective for elaborating long-term development scenarios. Current urgencies are fast changes of prices of commodities, market expansion using new interconnections as well as challenges of synchronization with other regions. These define the necessity to revise forecasts and scenarios.