Northern Oil & Gas (NOG) had the highest return between 2007 and 2010 by a mid-cap US stock, returning 8,788,187.5%.

ASSET	YEARS	% RETURN
Northern Oil & Gas (NOG)	2007-2010	8,788,187.5%
Boyd Group Services (BGSI)	2007-2010	720.97%
Amneal Pharmaceuticals, Inc Class A Common Stock (AMRX)	2007-2010	704.4%
Aura Minerals Inc Common Shares (AUGO)	2007-2010	668.67%
Imax (IMAX)	2007-2010	632.9%
ICL Israel Chemicals (ICL)	2007-2010	541.02%
Axogen (AXGN)	2007-2010	468.13%
Neogen (NEOG)	2007-2010	307.58%
Cal-Maine Foods (CALM)	2007-2010	286.17%
Pegasystems (PEGA)	2007-2010	281.88%
Baytex Energy (BTE)	2007-2010	274.85%
Perrigo (PRGO)	2007-2010	274.05%
Mosaic (MOS)	2007-2010	266.33%
Compania de Minas Buenaventura SAA ADR (BVN)	2007-2010	262.91%
OceanaGold (OGC)	2007-2010	256.19%
Hawkins (HWKN)	2007-2010	253.73%
Eldorado Gold (EGO)	2007-2010	238.01%
Dorman Products (DORM)	2007-2010	234.94%
Travere Therapeutics (TVTX)	2007-2010	233.33%
Cleveland-Cliffs (CLF)	2007-2010	230.96%
First Majestic Silver (AG)	2007-2010	219.12%
New Oriental Education & Technology (EDU)	2007-2010	213.18%
Ultrapar Participacoes SA ADR (UGP)	2007-2010	212.82%
Corcept Therapeutics (CORT)	2007-2010	206.35%
Balchem (BCPC)	2007-2010	205.96%

Mid-cap stocks are treated as having a market cap between $2B and $10B.