Url.RouteUrl("OpinionByCompany", new RouteValueDictionary(new{cid=newop.CompanyID,oid=newop.ID}), HttpContext.Request.Url.Scheme, HttpContext.Request.Url.Authority)
var relativeUrl = Url.Action("MyAction"); //..or one of the other .Action() overloads
var currentUrl = Request.Url;
var absoluteUrl = new System.Uri(currentUrl, relativeUrl);