What citation style allows the author to reference sources with superscript numbers? What citation style allows the author to reference sources with superscript numbers?

I'm at the very edge of my page limit. I'm allowed to use any citation style. I need something concise that can point to the relevant works I've listed on the works-cited page. 

Anyone have any suggestions?
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).