The problem of low performance in data extraction from data warehouse can becritical in the Business Intelligence projects because of the major impact in the using the datafrom data warehouse: if a BI report is taking a lot of time to run or the data displayed are nolonger available for taking critical decisions, the project can be compromised. In this paperwe present an overview of an implementation of a Business Intelligence project in a nationalcompany, the problems we confronted with and the techniques that we applied to reduce thecost of execution for improving query performance in this decisional support system. We’llpresent several techniques that we applied to reduce queries’ execution time and to improvethe performance of the BI analyses and reports.