(a) ADRs are listed on an American Stock Exchange. GDRs are listed in stock exchanges other than American Stock Exchanges.
(b) ADRs can be issued only to American citizens where as GDRs can be issued to non-American citizens also.
(c) ADR is mainly an institutional market with higher liquidity whereas GDRs are less liquid.
(d) ADR enhances shareholders value more than GDR.