This paper has two specific goals to achieve. The first goal is to address major challenges encountered in design and development of miniature hydrodynamic bearings for small form factor hard disk drive spindle motors. These challenges include extremely small thickness of the spindle motors, mass productivity of tiny bearing parts, and bearing reliability and performance in relation to changes in atmospheric pressure. To overcome these challenges, we have developed a prototype hydrodynamic bearing that is resistant to environmental changes, free from oil film disruption, and tolerant of variations in processing precision. The prototype hydrodynamic bearing has two special features: an oil circulation function and a gas/liquid separation function. The oil circulation function is achieved by using asymmetric hydrodynamic grooves together with circulation passages. The gas/liquid separation function is achieved by using tapered capillary seals in the circulation passages. As a result of these two special features, the prototype hydrodynamic bearing can successfully expel air bubbles out of the bearing, thus enhancing the performance and reliability of the hydrodynamic bearing. The second goal is to evaluate the prototype hydrodynamic bearing in a miniature spindle motor for small form factor hard disk drives. Two specific bearing designs are evaluated. The first bearing design is a pushing type that generates no low-pressure area. However, the flow rate increases at high temperature. The second design is just the opposite. It is a pulling type design that generates a low-pressure area. But the flow rate is constant and is independent of temperature changes. To accommodate manufacturing tolerances, a parametric study is conducted to identify the effects of manufacturing tolerance on bearing performance.