using System.Data.OracleClient;

string connString = "User ID=IFSAPP;Password=IFSAPP;Data Source=RACE;";
OracleConnection conn = new OracleConnection(connString);
try
{
  conn.Open();
  MessageBox.Show(conn.State.ToString());
}
catch (Exception ex)
{
  ShowErrorMessage(ex.Message.ToString());
}
finally
{
  conn.Close();
}

 using System.Data.OracleClient;

string connString = "User ID=IFSAPP;Password=IFSAPP;Data Source=(DESCRIPTION = (ADDRESS_LIST= (ADDRESS = (PROTOCOL = TCP)(HOST = 127.0.0.1)(PORT = 1521))) (CONNECT_DATA = (SERVICE_NAME = RACE)))";
OracleConnection conn = new OracleConnection(connString);
try
{
  conn.Open();
  MessageBox.Show(conn.State.ToString());
}
catch (Exception ex)
{
  ShowErrorMessage(ex.Message.ToString());
}
finally
{
  conn.Close();
}

using System.Data.OleDb;

string connString = "Provider=OraOLEDB.Oracle.1;User ID=IFSAPP;Password=IFSAPP;Data Source=(DESCRIPTION = (ADDRESS_LIST= (ADDRESS = (PROTOCOL = TCP)(HOST = 127.0.0.1)(PORT = 1521))) (CONNECT_DATA = (SERVICE_NAME = RACE)))";
OleDbConnection conn = new OleDbConnection(connString);
try
{
  conn.Open();
  MessageBox.Show(conn.State.ToString());
}
catch (Exception ex)
{
  ShowErrorMessage(ex.Message.ToString());
}
finally
{
  conn.Close();
}

using System.Data.OleDb;

string connString = "Provider=MSDAORA.1;User ID=IFSAPP;Password=IFSAPP;Data Source=(DESCRIPTION = (ADDRESS_LIST= (ADDRESS = (PROTOCOL = TCP)(HOST = 127.0.0.1)(PORT = 1521))) (CONNECT_DATA = (SERVICE_NAME = RACE)))";
OleDbConnection cnn = new OleDbConnection(connString);
try
{
  conn.Open();
  MessageBox.Show(conn.State.ToString());
}
catch (Exception ex)
{
  ShowErrorMessage(ex.Message.ToString());
}
finally
{
  conn.Close();
}

Oracle.RACE =
(DESCRIPTION=
  (ADDRESS_LIST=
   (ADDRESS=
    (PROTOCOL=TCP)
    (HOST=127.0.0.1)
    (PORT=1521)
   )
  )
  (CONNECT_DATA=
   (SID=RACE)
   (SERVER=DEDICATED)
  )
)

using Oracle.DataAccess.Client;

string connString = "DATA SOURCE=Oracle.RACE;PERSIST SECURITY INFO=True;USER ID=IFSAPP;password=IFSAPP";
OracleConnection conn = new OracleConnection(connString);
try
{
  conn.Open();
  OracleCommand cmd = new OracleCommand(cmdText,conn);
  OracleDataReader reader = cmd.ExecuteReader();
  this.DataGridView1.DataSource = reader;
  this.DataGridView1.DataBind();
}
catch (Exception ex)
{
  ShowErrorMessage(ex.Message.ToString());
}
finally
{
  conn.Close();
}

using Devart.Data.Oracle;

OracleConnection conn = new OracleConnection();
conn.ConnectionString = "";
conn.Unicode = true;
conn.UserId = "IFSAPP";
conn.Password = "IFSAPP";
conn.Port = 1521;
conn.Server = "127.0.0.1";
conn.Sid = "RACE";
try
{
  conn.Open();
  //execute queries, etc
}
catch (Exception ex)
{
  ShowErrorMessage(ex.Message.ToString());
}
finally
{
  conn.Close();
}