What citation style allows the author to reference sources with superscript numbers?
I am presuming this is a coursework assignment. If you're that tight for space, are you sure you haven't written too much? Be careful that your finished piece doesn't "feel" cramped.

The Nature journal uses superscript numbers for in-text citations1 and then references them in the bibliography like so:


Hynek, B. M. Implications for hydrologic processes on Mars from extensive bedrock outcrops throughout Terra Meridiani. Nature 431, 156–159 (2004).