The study is based on 4,413 papers identified from Elsevier’s Scopus for various fields from 2000 to 2004 to assess the research impact of OA journal articles, from DOAJ based journals, using sampling techniques following ‘R’ software. It focuses to test the hypothesis “OA articles in hard, urban and convergent fields receive more citations (hence higher research impact) than those in soft, rural and divergent subjects, besides a comparative study of research impact across disciplines, supported with experimental method and literature review.