According to The NPD Group (, a market research company, Apple’s iTunes store continued to lead all music retailers, with 28% of all music purchased by U.S. consumers — a gain of four percentage points since the first quarter of 2009.

Amazon gained three percentage points to tie Walmart for second position at 12%t. Based on NPD’s latest music industry research, sales of digital tracks and albums accounted for 40% of overall music market share in the first quarter (Q1) of 2010, which is a five percentage point gain since Q1 2009. NPD’s data is based on a combined music-retailer ranking that reflects the combined sales of CDs and digital music downloads (i.e., 12 digital music track downloads are equivalent to one CD).

When reviewing sales of digital music separately from CDs, NPD’s MusicWatch data revealed that iTunes’s share of the digital-music download retail market has remained essentially flat since Q1 2009 — growing just one percentage point to reach 70% of the digital music market last quarter. At the same time, AmazonMP3 grew by four percentage-points to reach 12%, while Amazon’s share of the CD market grew by two percentage points to reach 11%.

In NPD’s review of CD retailers, Walmart led U.S. CD purchases in Q1 2010 with 17% share of retail market. Best Buy followed Walmart with 14%, and Amazon’s 11 percent share positioned them in third place.