According to Official Guinness Records,
The largest observation (Ferris) wheel is the 167.5 m (594 ft 8.4 in) tall Las Vegas High Roller, located at the LINQ in Las Vegas, Nevada, USA. The wheel opened to the public on March 31, 2014, and features 28 spherical cabins each holding 40 people for a total capacity of 1,120 passengers. A full revolution of the wheel takes 30 minutes.
For a complete list of 2014 records, please visit 2014 Guinness Records in United States.