It is known that core damage is a crucial issue in rock testing, and, as a consequence, may have a large impact on several activities related to reservoir development -e.g. reserves estimation, sand production, reservoir compaction, etc. This is even more relevant for weak and unconsolidated formations as well as for laminated and fractured rock materials. Thus the possibility of evaluating and quantifying core damage may greatly improve data quality, predictions and performances. (Laboratory experiments on artificial rock samples, carefully prepared under controlled conditions to simulate target reservoirs, have shown that the damage due to the in-situ stresses release can be reduced if a certain bias load is applied and maintained on the top of the core while coring. Such observations have been also confirmed by numerical simulations performed using a Finite Element code. Based on these results, Security DBS designed and manufactured a new coring tool, named Core Stress Monitor (CSM), in which a piston device provides the adjustable bias load. The tool was successfully tested by coring unconsolidated sand reservoir formations showing that there are no operational differences when comparing CSM and a standard coring tool. Comparative laboratory experiments on samples cored both with CSM and a traditional coring assembly seem to confirm the validity of the CSM tool in reducing stress release induced damage.