The amount of PLN 15,423,740 is the value of compensation for which the Municipality of Kosakowo decided to file, with our firm’s assistance, against an underground gas storage project investor. The persons who are interested in pursuing major infrastructural projects would often endeavour to enter into specific arrangements with the local governments where the projects are intended for execution. Various issues tend to arise thereafter, in the course of implementing these arrangements; the claims raised by the Kosakowo Municipality can be an example of such issues. This leading case will not only define the terms of cooperation under civil law of public administration authorities and infrastructural project investors but also the terms of pursuing claims arising from such cooperation.