Though a relatively new development, swelling elastomers are now widely used in various difficult situations in the oil and gas industry such as water shutoff and other types of zonal isolation. Swell packers were initially used for repair of old and damaged wells, but they are now increasingly used for higher productivity and profitability through developments like slim well design and cementless completions. Current work employs finite element simulation to study tubular expansion and swelling elastomer packers in different downhole petroleum applications. This is the first study of its kind, investigating seal behavior based on material properties of expandable tubular and different swelling elastomers used in actual oil wells. Material properties of the un-expanded tubular and un-swelled elastomers are obtained through a series of tensile tests. Sealing pressure at the contact surface between elastomer and formation is studied for different parameters (elastomer material, tubular expansion ratio, seal length and thickness, formation type, etc). Higher values of elastomer stiffness, tubular expansion, and seal thickness result in higher seal contact pressure. Higher sealing pressure is also noted in the case when swell packer is expanding against a rigid rock formation. These predictions can be used for performance analysis and design improvement of solid expandable tubulars and swelling elastomer applications.