A self-expanding prosthesis delivery system comprising: an outer tubular structure having a proximal end portion and a distal end portion, said distal end portion configured to receive a self expanding prosthesis; an inner tubular member adapted for tracking over a guidewire, having a proximal end portion fixed to a handle and a distal end portion fixed to a first sealing member, and being disposed in said outer tubular structure; at least a portion of said outer tubular structure being movable relative to said inner tubular member such that at least a portion of said outer tubular structure can be retracted, while at least a portion of said inner tubular member is held in a fixed position relative to said outer tubing structure; said outer tubular structure and inner tubular member being radially spaced from one another so as to form a fluid fillable space having first and second ends; wherein said first sealing member is fixedly secured to said inner tubular member at a location proximal to said distal end portion to fluidly seal said first end of said fluid fillable space, said first sealing member extending from said inner tubular member to said outer tubular structure and being in sealing engagement with said outer tubular structure, and a second seal arranged at said second end of said fluid fillable space formed by said handle to fluidly seal the second end of said fluid fillable space, wherein said outer tubular structure, inner tubular member, first sealing member, and said second seal form a chamber, which has a constant volume that remains constant when said moveable portion of said outer tubular structure is retracted relative to said inner tubular member. an outer tubular structure having a proximal end portion and a distal end portion, said distal end portion configured to receive a self expanding prosthesis; an inner tubular member adapted for tracking over a guidewire, having a proximal end portion fixed to a handle and a distal end portion fixed to a first sealing member, and being disposed in said outer tubular structure; at least a portion of said outer tubular structure being movable relative to said inner tubular member such that at least a portion of said outer tubular structure can be retracted, while at least a portion of said inner tubular member is held in a fixed position relative to said outer tubing structure; said outer tubular structure and inner tubular member being radially spaced from one another so as to form a fluid fillable space having first and second ends; wherein said first sealing member is fixedly secured to said inner tubular member at a location proximal to said distal end portion to fluidly seal said first end of said fluid fillable space, said first sealing member extending from said inner tubular member to said outer tubular structure and being in sealing engagement with said outer tubular structure, and a second seal arranged at said second end of said fluid fillable space formed by said handle to fluidly seal the second end of said fluid fillable space, wherein said outer tubular structure, inner tubular member, first sealing member, and said second seal form a chamber, which has a constant volume that remains constant when said moveable portion of said outer tubular structure is retracted relative to said inner tubular member.