Par Pacific (PARR) had the highest return between 2010 and 2015 by a mid-cap US stock, returning 3,823.3%.

ASSET	YEARS	% RETURN
Par Pacific (PARR)	2010-2015	3,823.33%
ACADIA Pharmaceuticals (ACAD)	2010-2015	2,600.76%
Vipshop (VIPS)	2010-2015	2,444.97%
Travere Therapeutics (TVTX)	2010-2015	2,043.33%
Patrick Industries (PATK)	2010-2015	1,668.25%
Nexstar Broadcasting (NXST)	2010-2015	1,418.35%
Lithia Motors (LAD)	2010-2015	1,281.39%
Under Armour Inc A (UAA)	2010-2015	1,073.79%
CleanSpark (CLSK)	2010-2015	1,053.86%
Astronics (ATRO)	2010-2015	1,031.74%
Manhattan Associates (MANH)	2010-2015	987.88%
Boyd Group Services (BGSI)	2010-2015	910.19%
Silicon Motion Technology (SIMO)	2010-2015	909.66%
Alaska Air (ALK)	2010-2015	850.99%
Ligand Pharmaceuticals (LGND)	2010-2015	799.65%
MarketAxess (MKTX)	2010-2015	788.99%
American Airlines (AAL)	2010-2015	786.97%
Caesars Entertainment (CZR)	2010-2015	746.15%
Axos Financial (AX)	2010-2015	742%
Alkermes (ALKS)	2010-2015	738.23%
Ambarella (AMBA)	2010-2015	730.7%
U-Haul (UHAL)	2010-2015	729.02%
CVR Energy (CVI)	2010-2015	726.41%
Bath & Body Works (BBWI)	2010-2015	682.12%
Bausch Health Companies (BHC)	2010-2015	666.5%

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