Evolution of the Loop Current and the adjacent mesoscale rings have been 
investigated over a 20-day period, starting June 1, 1998. Observational data 
(altimetry, drifters) and a model velocity field (output of a Princeton Ocean 
Model of the Gulf of Mexico) were used in the study. The coherent structures 
were identified in the Lagrangian framework by means of Effective Invariant 
Manifolds (EIM). The Lagrangian approach provides detailed information about 
ring interaction and reveals features of the ring dynamics hidden in the 
Eulerian picture. During the observation period, a new ring was formed in the 
meander of the LC (area 2x10^4 km) and a large anticylonic ring west of it (area 
7x10^4 km) was cleaved by a southbound cyclonic eddy. The intensity of water 
exchange between the rings and the ambient water varied considerably among the 
rings: cyclonic rings experienced active mixing along the boundary, whereas the 
anticyclonic ones were relatively isolated. Available drifter trajectories are 
in qualitative agreement with the results of the Lagrangian analysis based on 
the model velocity field.