Using OleDbDataAdapter Update with InsertCommands and getting blocking locks on Oracle table

Question

The following code snippet shows the use of OleDbDataAdapter with InsertCommands.  This code is producing many inserts on the Oracle table and is now suffering from contention... all on the same table.  How does the OleDbDataAdapter produce
inserts from a dataset... what characteristics do these inserts inherent in terms of batch behavior... or do they naturally contend for the same resource. 
oc.Open();
for (int i = 0; i < xImageId.Count; i++)
// Create the oracle adapter using a SQL which will not return any actual rows just the structure
OleDbDataAdapter da =
   new OleDbDataAdapter("SELECT BUSINESS_UNIT, INVOICE, ASSIGNMENT_ID, END_DT, RI_TIMECARD_ID, IMAGE_ID, FILENAME, BARCODE_LABEL_ID, " +
   "DIRECT_INVOICING, EXCLUDE_FLG, DTTM_CREATED, DTTM_MODIFIED, IMAGE_DATA, PROCESS_INSTANCE FROM sysadm.PS_RI_INV_PDF_MERG WHERE 1 = 2", oc);
// Create a data set
DataSet ds = new DataSet("documents");
da.Fill(ds, "documents");
// Loop through invoices and write to oracle
string[] sInvoices = invoiceNumber.Split(',');
foreach (string sInvoice in sInvoices)
    // Create a data set row
    DataRow dr = ds.Tables["documents"].NewRow();
    ... map the data
    // Populate the dataset
    ds.Tables["documents"].Rows.Add(dr);
// Create the insert command
string insertCommandText =
    "INSERT /*+ append */ INTO PS_table " +
    "(SEQ_NBR, BUSINESS_UNIT, INVOICE, ASSIGNMENT_ID, END_DT, RI_TIMECARD_ID, IMAGE_ID, FILENAME, BARCODE_LABEL_ID, DIRECT_INVOICING, " +
    "EXCLUDE_FLG, DTTM_CREATED, DTTM_MODIFIED, IMAGE_DATA, PROCESS_INSTANCE) " +
    "VALUES (INV.nextval, :BUSINESS_UNIT, :INVOICE, :ASSIGNMENT_ID, :END_DT, :RI_TIMECARD_ID, :IMAGE_ID, :FILENAME,  " +
    ":BARCODE_LABEL_ID, :DIRECT_INVOICING, :EXCLUDE_FLG, :DTTM_CREATED, :DTTM_MODIFIED, :IMAGE_DATA, :PROCESS_INSTANCE)";
// Add the insert command to the data adapter
da.InsertCommand = new OleDbCommand(insertCommandText);
da.InsertCommand.Connection = oc;
// Add the params to the insert
da.InsertCommand.Parameters.Add(":BUSINESS_UNIT", OleDbType.VarChar, 5, "BUSINESS_UNIT");
da.InsertCommand.Parameters.Add(":INVOICE", OleDbType.VarChar, 22, "INVOICE");
da.InsertCommand.Parameters.Add(":ASSIGNMENT_ID", OleDbType.VarChar, 15, "ASSIGNMENT_ID");
da.InsertCommand.Parameters.Add(":END_DT", OleDbType.Date, 0, "END_DT");
da.InsertCommand.Parameters.Add(":RI_TIMECARD_ID", OleDbType.VarChar, 10, "RI_TIMECARD_ID");
da.InsertCommand.Parameters.Add(":IMAGE_ID", OleDbType.VarChar, 8, "IMAGE_ID");
da.InsertCommand.Parameters.Add(":FILENAME", OleDbType.VarChar, 80, "FILENAME");
da.InsertCommand.Parameters.Add(":BARCODE_LABEL_ID", OleDbType.VarChar, 18, "BARCODE_LABEL_ID");
da.InsertCommand.Parameters.Add(":DIRECT_INVOICING", OleDbType.VarChar, 1, "DIRECT_INVOICING");
da.InsertCommand.Parameters.Add(":EXCLUDE_FLG", OleDbType.VarChar, 1, "EXCLUDE_FLG");
da.InsertCommand.Parameters.Add(":DTTM_CREATED", OleDbType.Date, 0, "DTTM_CREATED");
da.InsertCommand.Parameters.Add(":DTTM_MODIFIED", OleDbType.Date, 0, "DTTM_MODIFIED");
da.InsertCommand.Parameters.Add(":IMAGE_DATA", OleDbType.Binary, System.Convert.ToInt32(filedata.Length), "IMAGE_DATA");
da.InsertCommand.Parameters.Add(":PROCESS_INSTANCE", OleDbType.VarChar, 10, "PROCESS_INSTANCE");
// Update the table
da.Update(ds, "documents");

Answer 1

Here is what Oracle is showing as blocking locks and the SQL that has been identified with each of the SIDS.  Not sure why there is contention.  There are no triggers or joined tables in this piece of code.
Here is the SQL all of the SIDs below are running:
INSERT INTO sysadm.PS_RI_INV_PDF_MERG (SEQ_NBR, BUSINESS_UNIT, INVOICE, ASSIGNMENT_ID, END_DT, RI_TIMECARD_ID, IMAGE_ID, FILENAME, BARCODE_LABEL_ID, DIRECT_INVOICING, EXCLUDE_FLG, DTTM_CREATED, DTTM_MODIFIED, IMAGE_DATA, PROCESS_INSTANCE) VALUES (SYSADM.INV_PDF_MERG.nextval,
:BUSINESS_UNIT, :INVOICE, :ASSIGNMENT_ID, :END_DT, :RI_TIMECARD_ID, :IMAGE_ID, :FILENAME, :BARCODE_LABEL_ID, :DIRECT_INVOICING, :EXCLUDE_FLG, :DTTM_CREATED, :DTTM_MODIFIED, :IMAGE_DATA, :PROCESS_INSTANCE)
SID 1452 (BTSUSER,BIZTPRDI,BTSNTSvc64.exe) in instance FSLX1 is blocking SID 1150 (BTSUSER,BIZTPRDI,BTSNTSvc64.exe) in instance FSLX1
SID 1452 (BTSUSER,BIZTPRDI,BTSNTSvc64.exe) in instance FSLX1 is blocking SID 1452 (BTSUSER,BIZTPRDI,BTSNTSvc64.exe) in instance FSLX1
SID 1452 (BTSUSER,BIZTPRDI,BTSNTSvc64.exe) in instance FSLX1 is blocking SID 1156 (BTSUSER,biztprdi,BTSNTSvc64.exe) in instance FSLX3
SID 1452 (BTSUSER,BIZTPRDI,BTSNTSvc64.exe) in instance FSLX1 is blocking SID 6 (BTSUSER,BIZTPRDI,BTSNTSvc64.exe) in instance FSLX2
SID 1452 (BTSUSER,BIZTPRDI,BTSNTSvc64.exe) in instance FSLX1 is blocking SID 1726 (BTSUSER,BIZTPRDI,BTSNTSvc64.exe) in instance FSLX2
SID 1452 (BTSUSER,BIZTPRDI,BTSNTSvc64.exe) in instance FSLX1 is blocking SID 2016 (BTSUSER,biztprdi,BTSNTSvc64.exe) in instance FSLX2