We developed a novel organic-inorganic hybrid that composed of various organic moieties covalently linked with nanometer thick inorganic platelets. The synthesized compounds are highly pure and have reproducible chemical compositions. These hybrids are employed as viscosifier in oil-based drilling fluids. The rheological behavior was studied at ambient condition as well as under high pressure and high temperature. A facile, one-pot synthetic route generate nanometer sized layered materials with covalently bound organic functionalities, as confirmed by X-ray powder diffraction and Infrared spectroscopy. An unprecedented improvement in flat rheology was observed under high pressure (10000 psi) and temperature up to 300°F as compared to commercial organoclays. The temperature dependent viscosity and viscoelastic properties of the fluids are also demonstrated. It has been challenging to obtain flat rheological behavior under high pressure and temperature by using commercial organoclays. A flat rheological behavior is achieved by incorporating organic-inorganic hybrids in drilling fluids.